I agree with the above poster. I keep my TV on at night. When I get tired I turn the volume almost all the way down. If you don't want to sleep with the TV on you can always try listening to the radio on a calming station.
Have you tried hypnotherapy? I do not have issues with PTSD nor do I have any experience, but I do have issues with insomnia and a deep-rooted fear, since childhood, of going to bed and going to sleep. Similar to you, I fear something bad happening while I'm not awake and alert. There are hypnotherapy CDs to help you fall asleep and relax you and there are also CDs specific for fears and anxiety. It wouldn't hurt to give them a try. The mind is a powerful healing tool and sometimes it just takes a little retraining along with the meds and other positive lifestyle changes.
Good luck to you!!